1. Field of the Invention
The present invention relates to a map database apparatus which, preferably mounted in a navigation system for vehicles and the like, is used in road map display, map matching, calculation of a recommended route and the like.
2. Description of the Prior Art
Vehicular navigation systems in the known art are provided with a function for displaying a road map of the area where the vehicle is currently located, a function for accurately detecting the vehicle position through map matching, a function for calculating a recommended route from a point of departure to a destination and the like. In these vehicular navigation systems in the prior art, data for road map display, data for map matching and data for route search are separately stored in a CD-ROM or the like in order to maintain compatibility with existing software programs and also to improve the processing speed.
The data for road map display includes the widest range map data which has the smallest scale and is for displaying the widest range area, and the most detailed map data which has the largest scale and is for displaying the most narrow range area in detail, and a plurality of map data which have various scales between the widest range map and the most detailed map. For example, the widest range map data is denoted as data of level 4, the most detailed map data is denoted as data of level 1, and data between level 4 and level 1 are denoted as data of level 3 and data of level 2, respectively.
FIGS. 25A and 25B explain the road map of the data for road map display which is stored as above mentioned level 4 and level 3. The CD-ROM stores the data for road map display of level 4 and the data for road map display of level 3 respectively. FIG. 25A shows a road map of a mesh M4 in level 4, and in this mesh M4 one road D1 and two roads D2 and D3 which are connected to intersections C1 and C2 located at both ends of the road D1 are shown. A small area m3 in level 4 which is hatched and is one of 16 parts into which the mesh M4 is divided) corresponds to a mesh M3 in level 3. As shown in FIG. 25B, a road D4 which is a part of the road D1 is only shown in the mesh M3.
For example, if a detail button is operated when the road map of the mesh M4 of level 4 is displayed on a monitor, then the road map of the mesh M3 of level 3 is displayed. In this case, however, an identifying data which shows that the road D1 and the road D4 are identical is not used. Consequently, it is difficult to know that they correspond to each other between the levels. And also, there is the same problem in the data for route search. In recommended route data which results from route search, it is difficult to know which portions are corresponding to each other between data which results from route search in level 2 and data which results from route search in level 4. Further, since identifying data which shows the identical road between the data for road map display and the data for route search is not used, it is difficult to know the correspondence of the identical road when the recommended route data is interposed onto the data for road map display.